Viscous liquids are applied by dispensers onto substrates in a variety of dispensing applications employed in the manufacture of products and product packaging. These viscous liquids include thermoplastic materials such as hot melt adhesives. Liquid dispensers utilize pneumatically or electrically actuated valve assemblies for metering a precise quantity of the viscous liquid and discharging the metered amount through a discharge outlet. Many thermoplastic materials exist in a solid form at room or ambient temperature and must be heated to create a flowable viscous liquid. Typically, the solid form of material is placed in a holding tank having heated walls and is melted by heating the solid material above its melting point. The viscous liquid is pumped in a molten state under pressure from the holding tank through a supply conduit to a manifold block. The manifold block has liquid passageways connected in liquid communication with the dispensing orifice of one or more liquid dispensers.
Such liquid dispensers, consisting of a manifold and a dispensing module, can often be mounted on small, or table-top, robots that are controlled to accurately position the dispenser and to precisely meter the application of a viscous liquid, such as adhesive, solder, underfill material, or other liquids. The dispensers are also coupled with a supply line that provides the liquid under pressure from an appropriate supply. In most applications involving the dispensing of a heated viscous liquid, the liquid supply line will be warmed by heating elements to compensate for heat loss as the liquid travels from the liquid supply source to the liquid dispensing module. Thus, the liquid supply lines are bulky in order to withstand the pressure of the liquid and, additionally, include integral heating elements that add to both the size and weight of the supply lines.
As a result, the robot that controls the movement of the liquid dispenser is sized to handle the weight of the liquid supply lines, not just the liquid dispenser. Furthermore, the additional weight of the liquid supply lines limits the speed at which the robot can move because of increased inertia that adversely affects the precision of robot positioning at higher speeds. The presence of heated liquid supply lines must also be considered when designing a workspace for a liquid dispensing system as the supply lines must extend from the liquid dispenser to the heated holding tank without interference.
In the past some liquid dispensing systems have included a dispenser having a replaceable cartridge that can be periodically replaced by an operator when empty. To be practical, such an approach requires the replaceable cartridges to be manufacturable at an economic cost and available at sufficient quantities so as to not adversely affect operation of the liquid dispensing system. Thus, such a cartridge approach has not been used within an adhesive hot melt liquid dispenser environment.
Accordingly, a need exists for a robot-mounted liquid dispenser, particularly an adhesive hot melt liquid dispenser that does not utilize a liquid supply line to couple the liquid dispenser to a remote liquid source, such as a tank. Satisfaction of this need would provide such benefits as removing hoses and swivels in a work area, improving robot dexterity, and reducing the overall tooling load of the robot and, thus, its required size. Additionally, supply hoses can be avoided that have flexibility and resiliency which sometimes cause surges in the amount and pressure of liquid arriving at a manifold resulting in inaccurate liquid metering.